A cable television (CATV) network serves to broadcast television (TV) content to home viewers. Many cable TV networks utilize a hybrid fiber-coaxial (HFC) infrastructure, which combines a fiber optic network with a coaxial cable network. The fiber optic network extends from the cable TV headend to regional distribution hubs and to optical nodes, each of which may service up to around 2,000 subscribers. The coaxial cable network extends from the optical node to the subscriber home, via main trunk cables and smaller distribution cables in a tree and branch configuration. The optical node includes an optical signal receiver for converting the optically modulated TV signal originating at the headend into an electrical radio frequency (RF) modulated signal, to be distributed downstream to the subscriber homes via the coaxial cables. The optical node may also transmit information in the reverse path upstream from the subscriber home to the cable TV headend. RF amplifiers are distributed along the trunk and distribution coaxial cables, for overcoming the attenuation and passive losses of the downstream (or upstream) RF signal. The coaxial cable network also carries alternating current (AC) power, which is added to the trunk cable line (usually at 60V or 90V) by a power supply and power inserter, supplying power to the trunk and distribution RF amplifiers. Line extenders (smaller distribution amplifiers) may be used to boost the signals in order to maintain the power at a sufficient level when it reaches the television. A secondary line (or drop) connects the distribution line to the subscriber home through a “tap”, which passes the RF signal to the television sets for broadcasting, and supplies the AC power to devices which may require it. An HFC based network may also be used to provide telephone service, Internet access and other services in addition to television content broadcasting.
The network power supply may utilize a voltage stabilizer, such as a ferroresonant transformer, for providing a constant output voltage from the mains power source. The power supply generally provides 60V-90V AC at a frequency of 50/60 Hz. Due to resistance, the voltage level along the coaxial cable lines may drop below the minimum level required for the stable operation of the amplifiers and optical nodes. The standard approach for overcoming this voltage drop involves inserting additional power supplies (or transformers) to the network, to supply the extra power through a sorter coaxial cable. This approach, however, increases the number of network components and utility power connections, thereby substantially increasing the overall cost of the system. The added power supplies are also generally underutilized (serving a limited number of loads and required infrequently), resulting in overall inefficiency and wasted costs.
Reference is now made to FIGS. 1A and 1B. FIG. 1A is a schematic illustration of a hybrid fiber-coaxial (HFC) network infrastructure, generally referenced 10, which is known in the art. FIG. 1B is a schematic illustration of another HFC network infrastructure, generally referenced 60, which is known in the art. HFC network infrastructure 10 includes an optical node 12, a first power source 14, a first power inserter 16, a second power source 18, a second power inserter 20, a plurality of trunk amplifiers 22, 24 and 26, and a plurality of line extenders 28, 30, 32, 34, 36 and 38. Optical node 12 is connected to trunk amplifiers 22, 24 and 26 via coaxial cables 40, 42 and 44, respectively. Trunk amplifier 22 is connected to line extenders 28 and 30 via respective coaxial cables 46 and 48. Trunk amplifier 26 is connected via coaxial cable 50 to line extender 34, which is connected to line extender 32 via coaxial cable 52. Trunk amplifier 26 is connected via coaxial cable 54 to line extender 36, which is connected to line extender 38 via coaxial cable 56. Power source 14 provides power via power inserter 16 through coaxial cable 44, supplying optical node 12, trunk amplifiers 22, 24 and 26, and line extenders 28, 30, 32 and 34 with sufficient power to operate. Second power source 18 reduces the current load on power supply 14, providing sufficient power for line extenders 36 and 38, all of which are distant from first power source 14, thereby compensating for the large voltage drop over coaxial cable 44. Power source 18 provides power via power inserter 20 through coaxial cable 54.
With reference to FIG. 1B, HFC network infrastructure 60 is analogous to HFC network infrastructure 10, except for a third power source 15 connected to coaxial cable 44 via third power inserter 17. Third power source 15 is disposed in proximity to first power source 14, and supplies power to trunk amplifier 26, while first power source 14 supplies power to optical node 12, trunk amplifier 22 and 24, and line extenders 28 and 30, and second power source 18 supplies power to line extenders 32, 34, 36 and 38. The use of two power sources in close proximity is common when the total load power requirement exceeds the power obtainable from a single power source.
U.S. Pat. No. 5,747,888 to Zilberberg, entitled “Back up system for the supply of voltage in television cable systems”, is directed to a is back-up system for supplying voltage to main and secondary amplifiers in a cable television network in the case of an electricity fault. Each trunk line in the cable television network includes a switching means (e.g., an AC relay), which is connected (via power inserters) to both a local power supply and a second back-up power supply located near a neighboring trunk amplifier. When an electricity fault occurs, the switching means is automatically activated and electricity is supplied to the trunk amplifiers from the available power supply of a neighboring trunk. A pair of two-way back-up units may be located between a pair of adjacent trunks (e.g., the last two trunks of a cascade) operating in opposite directions to each other. During an electricity fault in one trunk, the two-way back-up unit connected to the adjoining trunk is activated and supplies voltage to the trunk where the fault occurs. When back-up voltage is no longer required, current flow from the back-up unit is terminated.
U.S. Pat. No. 5,844,327 to Batson, entitled “Apparatus and method for optimizing power distributed in a broadband signal system”, is directed to a broadband system (e.g., a CATV system) with optimized power distribution. Each fiber/coaxial distribution node includes a power supply and a combiner. The power supply includes an AC distribution panel, input rectifiers, power inverters and a controller. The AC distribution panel provides utility AC power to the rectifiers, where it is converted to a DC voltage, followed by inversion and conditioning by the inverters. The combiner provides the output power, together with broadband signals received from a trunk transceiver, to be distributed through the coaxial cable. The output power supplies power to operate amplifiers and network interface units in the broadband system. The controller monitors control and status information with power supply units in order to detect system operation errors. The power supply may be redundant bus-switched, where the mains, back-up batteries and auxiliary power units are diode isolated from each other and connected to the output via a redundant power bus, allowing continuous operation during failure, removal or maintenance of the rectifier or DC auxiliary source.
U.S. Pat. No. 5,845,190 to Bushue et al, entitled “Cable access device and method”, is directed to an access device that supplies combined communication and power signals to respective subscriber equipment facilities over a broadcast distribution network. The access device receives an RF communication signal and an AC power signal from an upstream section of a coaxial distribution cable, and isolates the communication signal from the power signal using a diplexer circuit. The isolated AC power is rectified and applied to a flyback converter controlled by a variable duty cycle control circuit directed by a transistor switch, which periodically connects a primary winding of a transformer to the input voltage, producing a DC output voltage. A load storage capacitor maintains the DC output voltage at a constant level sufficient to withstand momentary drops in the input AC power signal. Control circuitry adjusts the duty cycle of the transistor switch and the transformer switching cycle period, to maintain sufficient output power with a single stage conversion. A second diplexer circuit recombines the output voltage with the communication signal, and the recombined signal is reinserted onto a downstream section of the coaxial distribution cable for transmission.
U.S. Pat. No. 6,836,898 to Yates et al, entitled “Subscriber power module for CATV customer interface equipment”, is directed to a user interface apparatus for a CATV system with reduced energy consumption. The user interface apparatus includes an interior unit and an exterior unit disposed at the customer location. The interior unit receives high voltage AC power input (e.g., 110V) from a standard consumer power source, and converts it into a lower AC voltage (e.g., 30-60V). The lower AC voltage is provided to the coaxial cable and used to power electronic equipment in the interior unit and well as other equipment connected to the cable (such as in the exterior unit). The exterior unit receives high voltage AC power from a first coaxial cable (distributed by the CATV network), and low voltage AC power from a second coaxial cable (supplied by the interior unit). An AC power isolator electrically isolates the first coaxial cable from the low voltage AC power while conducting RF signals bidirectionally between the two cables. The isolator also isolates the high voltage AC power from damaging electronic equipment in the unit. The interior or exterior units may include a DC power supply for converting the AC voltage to DC voltages for operating electronic equipment.